Water treatment devices for home and other use are well known in the art. Such devices are incorporated into a water system either in-line or at a terminal end. An example of the former would be an under-the-counter device which filters water prior to reaching the faucet. There are two common types of terminal end devices--countertop and faucet-mounted. As compared to countertop and under-the-sink devices, designing a faucet-mounted device presents special challenges. These include making the device sufficiently light so that it can be attached to a faucet and sufficiently compact so that the device does not take up valuable sink space.
Water treatment devices can treat water by the use of mechanical filtration or chemical treatment. Mechanical filters treat water by preventing passage of particulates. As a mechanical filter approaches the end of its useful life, reduced or stopped flow due to particulate accumulation provides a ready indication that element replacement is necessary. By contrast, when the capacity of a chemical element is exceeded, there is no such indication. Chemical treatment is accomplished by processes such as adsorption (e.g. charcoal media) and ion exchange (e.g. for lead removal). Such chemical treatment eventually degrades and becomes inactive. However, no indication is provided to the user that the water is no longer being treated by the media.
As a result, various approaches have been taken to indicate end of life to the user where it is not inherently provided by the behavior of the filter media. One example is shown in U.S. Pat. No. 4,686,037. In this approach, a pre-filter is used to entrap contaminants, and the color of the pre-filter is compared by the user with a reference strip to determine when the media requires replacement. The problem with this approach, however, is that it is inherently subjective, and therefore subject to error. Also, the user can easily forget to check the reference filter and mistakenly believe the media is still purifying when it is not.
A much more accurate and foolproof means of indicating end of life is through totalizing the volume which has passed through the media and automatically shutting off flow after a predetermined volume has passed through the device. Although the flow totalization and shutoff valve mechanisms required are relatively expensive and complex, this has become recognized as the most accurate means of indicating end of life. For example, the certifying agency in the United States for water treatment devices, the National Sanitation Foundation, requires for certification of a rated volume, twice the filter media capacity when an automatic shutoff is not used, and only 20% additional capacity when an automatic shutoff is employed.
Both electrical and mechanical approaches to flow totalization are known in the prior art. Examples of the former are shown in U.S. Pat. Nos. 4,918,426 and 5,089,144. In this approach, flow rate is measured by, for example, a pressure transducer and then integrated to calculate total volume. After a predetermined volume has been reached, a valve is electrically actuated to stop flow.
Examples of mechanical totalization in water treatment devices are shown in U.S. Pat. Nos. 4,681,677 and 4,698,164. In the mechanical approach, typically a turbine powered by water flowing through the device is interconnected with a series of gears which mechanically "add up" the volume of water which has passed through the device. In turn, the gearing mechanism is interconnected with a valve such that, after a predetermined volume of water has passed through the device, the valve is mechanically actuated to stop flow through the device.
However, prior art mechanical automatic shutoff mechanisms suffer from certain shortcomings. One problem is that the mechanisms employed, such as in the '677 patent, are too bulky to be included in a compact device. Another problem with prior art devices is that they make resetting the totalization and shutoff mechanism unnecessarily difficult and/or expensive. For example, to reset the device shown in the '677 patent, one would apparently have to manually release the valve from the rotating cam and manually disengage the gearing mechanism to reset the totalization mechanism to a zero volume position. In the '164 patent, the valve shutoff mechanism is incorporated into the replaceable cartridge, and the shutoff valve is connected to the gearing mechanism upon replacement of the cartridge. This approach is unnecessarily wasteful and expensive because the shutoff valve is thrown away with each cartridge, rather than being reused.
With respect to faucet-mounted water treatment devices, it is not known in the prior art to incorporate automatic shutoff end-of-life indication. This is due at least in part to the obstacles associated with incorporating a mechanical flow totalization and shutoff mechanism in the required compact size. As a result, prior art devices have employed much cruder forms of end-of-life indication, such as that discussed above in the '037 patent. Not only are prior art end-of-life indicating devices much less accurate, but they are also unnecessarily wasteful due to the more frequent cartridge replacement often required by certification standards.
A feature that is common to faucet-mounted devices is the ability to bypass or divert water from the filter media so that untreated water can be obtained from the faucet. This is desirable because it avoids unnecessary use of the filter media, allowing the user to bypass the water treatment device if the water is not intended for drinking, as for example for washing hands or dishes.
Such a bypass mechanism is shown in the '037 patent. In this approach, a separate handle is attached to the opposite end of the mounting member to control a bypass valve. Other prior art devices use this same approach, and therefore suffer from certain disadvantages. The separate handle adds unnecessary complexity and expense to manufacturing a bypass mechanism. Also, because of the environment in which faucet-mounted devices are employed, there is a significant problem with keeping such devices clean. A separate handle only makes this more difficult, adding increased surface area and creating difficult-to-clean crevices. Finally, the added handle makes the appearance of the device less appealing, which is a particularly important concern for faucet-mounted devices.
What has been needed is a compact, low-cost and easy-to-manufacture water treatment device having an automatic shutoff mechanism which is easy to reset. What has also been needed is a faucet-mounted device incorporating automatic shutoff and a simple bypass mechanism.
What has also been needed is a replacement filter cartridge which can reset the flow totalization and shutoff mechanism upon replacement of the cartridge and which provides a simple water flow path and efficient sealing in communication with the water treatment device.